Contact testing device



July 8, 1941. H, MOcONNE-LL I 2,248,545

CONTACT TESTING DEVICE Filed Dec. so, 1939 u ALARM //4 'IHII INVENTOR J. H. MC CONNELL er ATTORNEY Patented July 8, 1941 UNITED STATES PATENT OFFICE John lVIcConnell, West 'Brig'htoh, N. Y., "assignor to Bell Telephone Laboratories, In'cjorporate'd'; N ew York, N I Y., a corporation of New' "York Application December 30, 1939, SerialNo. 311,730

" '7 Claims. j (Cl. 179-1752) This invention relates-to meansfor testing contact-operating mechanisms and more particularly to-mea'ns for indicating rebounds of the contact element of a telephone dial.

Inthe operation of circuit controlling contact devices the movable contact spring tends to rebound due to such causes as -resili'ency,'momentum, etc. In theca'se oftelephone dials or-pulsing mechanisms, this rebounding of the contact openings 'in the pulses generated by telephone dials and thus to detect improperly dials. I

This object is attained in'accordance with 2.

operating feature of the invention by the provision of means which function to detect and to furnish a positive indication of the occurrence of a prematureopening of the pulse generating" 'contacts-of a telephone dial and which discriminate between such premature opening and the standard opening which occurs at the end-of-a pulse. More specifically, the means resorted to comprise a gas-filled triode having an alarm "control relay in its plate circuit and-a pair of serially connected relays, controlled by the dialpulsin'g contacts, which cooperate to render the triode conductive only upon the occurrence of a premature opening of the dial contacts and to preclude the possibility of the alarm control relay operating when the contacts open at the end-of a pulse.

The invention will be readily understood from the following detailed description made with reference to the accompanying drawing, the single figure of which illustrates the circuit arrangement embodying the features of the invention.

In the following description made with reference to the drawing, it will be assumed that the pulsing spring 10 of dial D closes and remains closed without any rebounding for the duration of the pulse period. Upon closure of the spring Ill upon its associated contact an obvious circuit including the serially connected windings of relays R1 and R2 iscompleted. It will be observed that normally the plate and grid elec trodes of the triode V are disconnected from their respectivebattery supplies H and I2, the

plate circuit being 'open'at' the armatureand contactof relay- R1 and the gridcircuit being open at the armature and contact of relay R2.

Relay R2 is designed to operate and release faster "than relay R1. Upon closure ofthe dial contact, therefore, relay Rl will connect plate-battery H to the plate electrode of tube V by way of the left winding of relay R5 immediately after relay R2 functions to connect battery ii to the grid of tube V. The potentials of batteries H and I2 are such that under the condition just described the tube 'V-is blocked and does not fire, so that no current flows in the plate circuit. This condition prevails as long as the dial contact remains closed, so that rclay;Ra whose operating winding is included-in the plate circuit of tube- V does not operate.

At theend of the pulse'period, thedial spring lilfleaves its associated contact, thusopening the circuit to relays R1 and R2. Relay 'Ra'being'designed to restore faster than relay R1 releases its armature before relay R1 restores its armature. The plate'bircuit of tube V is therefore maintainedcomplet'e while the blocking biasof battery 12 is-removed from the grid of tube V. Relay R3, however, does not operate because it is designed so 'as to require a longer time for its operation than is required for the release of relay-R1; "It'follows therefore -'that though the plate circuitof tubeV is-momentarily energized, the operating winding'of relay R3 does not receive sum'ci'entcurrent to-operatethe relay before relay R1 releases its armature and opens the plate-circuit. 'Relay R3 does not operate therefore, to bring in analarm when the dial contact "spring functions without rebounding.

' It'willInow be assumed that, after the closure of th'e dial spring [0- on its associated contact, the 'contacts'open momentarily as in asecondar'y tor preliminary ppeningr 'The circuit for the windings-of relays R1 and R; is opened at the dial contacts and relay R2 being a speed relay, immediately releases its armature, but relay R1 being relatively slow releasing, maintains its armature contact closed. "Relay R2 in rel-easing its armature opens the grid battery circuit thus removing the blocking potential from the grid of tube At the end of the'momentary open,

ing of said contacts occurring at the end of a pulse and a preceding premature opening occurring subsequent to the initial closure of said contacts whereby said triode is rendered conductive during the occurrence of the premature opening and the alarm control relay accordingly operated.

2. A device for detecting rebounds of contacts whose initial closure initiates the transmission of a useful pulse, comprising a gas-filled triode,

an alarm control relay included in the plate circult of said triode and means for discriminating relay R3 remains operated after relay R1 restores 1 its armature at the end of the pulse period. The operation of the alarm Hi indicates to the test man that the contact device or dial under test is imperfect in that it does'not transmit true pulses.

The operate and release characteristics of relays R1, R2 and R3 are critical in the sense that the relays must function in definite time periods relative to one another. For example, relay R2 must be a speed relay so as to operate ahead of relay R1 when the dial contact is closed and must release immediately upon opening of the dial contact. If relay. R2 cannot release in the period of the secondary opening, no alarm will be given. The release time of relay R2 should, therefore, be fast enough to detect the minimum amount of secondary opening which is objectionable. Relay R1 must take longer to release 7 than relay Rzso that the arrangement may discriminate between a secondary open and the standard open at the end of a pulse period. The operate time of relay R3 should be a littlelonger than the release time of relay R1 less the release time of relay R2. If the difference is too large, a secondary opening at the end of the pulse will not be registered as relay R3 will not have time to operate before relay R1 fall off.

Fromthe foregoing description it is apparent that any secondary opening having a duration equal to or greater'than the objectionable minimum openingand less than the standard opening occurring at the end of a pulse period is detected and a positive indication thereof provided, and

that the duration of the minimum objectionable opening is determined. by the release time of relay R1. It is also apparent that the operate time of relay R2 determines the period of time after the initial closure of the spring ID on its contact during which rebounding cannot be detected. It has been found, however, that any rebounding of the contacts at the very start of the pulse period is of a high frequency nature as distinguished from a positive secondary opening and does not objectionably effect the pulse generated by the dial, so that a dial which might be characterized by such high frequency openings at the start of the pulse period need not berejected as faulty. Irrespective of this fact, it has also been found that any dial which produce secondary openings at the very start or finish of the pulse period is always characterized by subsequent secondary openings in pulses of the same train which are readily detected by the circuit arrangement herein described and consequently no defective dials will be passed when tested with the arrangement disclosed.

What is claimed is:

1. A device for detecting rebounds of contacts whose initial closure initiates the transmission of a useful pulse, comprising a gas-filled triode, an alarm control relay included in the plate circuit of said triode and apparatus controlled by said contacts for. discriminatingbetween an openbetween an opening of said contacts of predetermined duration and an opening thereof of less than the predetermined duration whereby the plate circuit of said triode is effectively completed and said alarm control relay operated only upon the occurrence of an opening of less than the predetermined duration, said means comprising a pair of serially connected relays controlled by said contacts and having distinctive time operate and release characteristics.

. 3, In a device for detecting rebounds of the contact springs of a circuit controlling device, an alarm control relay, a gas-filled triode having a plate circuitincluding the operating winding of said alarm control relay, and means responsive to a closure of said contact springs for completing said plate circuit and applying a blocking potential to the control electrode of said triode, whereby said alarm control relay is rendered inoperative upon closure of said contact springs, said means functioning upon a rebound of said contact springs to remove the blocking potential from the control electrode of said triode for the duration of the rebound without interrupting the continuity of the plate circuit of said triode whereby said alarm control relay operates to indicate the rebound.

4. In a device for detecting rebounds of the contact springs of a circuit controlling device, an alarm control relay, a gas filled triode having a plate circuit including the operating winding of said alarm control relay, and means responsive to a closure of said contact springs for completing said plate circuit and applying a blocking potential to the control electrode of said triode whereby said alarm control relay is rendered inoperative upon closure of said contact springs, said means functioning upon a rebound of said contact springs to remove the blocking potential from the control electrode of said triode for the duration of the rebound without interrupting the continuity of the plate circuit of said triode, whereby said alarm control relay operates to indicate the rebound, and said means also functioning when said contacts open for a predetermined interval of time after the initial closure thereof to remove the blocking potential from the control electrode of said triode and open the plate circuit thereof.

5. In a device for detecting rebounds of the contact springs of a circuit controlling device, an alarm control relay, a gas-filled triode having a plate circuit including the operating winding of said alarm control relay, and. means responsive to a closure of said :contact springs for completing said plate circuit andapplying a blocking potential to the control electrode of said triode whereby said alarm control relay is rendered inoperative upon closure of said contact spings, said means functioning upon a rebound of said contact springs. to remove the blocking potential from the'control electrode of said triode for the continuity of the plate circuit of said triode,

whereby said alarm control relay operates to indicate the rebound, said means comprising a pair of serially connected relays controlled by said contact springs, one of said relays having faster operate and release characteristics than the other.

6. A device for testing a telephone dial for rebounds of the pulsing contacts thereof comprising a gas-filled triode, a source of blocking potential for the control electrode of said triode, an alarm control relay included in the plate circuit of said triode, a first relay operating in response to a closure of the pulsing contacts of the dial for connecting said source of blocking potential to the control electrode of said triode, a second relay connected in series with said first relay and having a time operate characteristic such that it operates subsequently to the operation of said first relay upon closure of the pulsing contacts to complete the plate circuit of said triode, whereby said triode is rendered non-conducting and said alarm control relay inoperative, said second relay having a time release characteristic such that it remains operated when the pulsing contacts rebound to momentarily open the series circuit including the windings of said first and second relays and to cause said first relay to release and remove said blocking potential from the control electrode of said triode whereby said triode is rendered conducting and causes said alarm control relay to operate to indicate the occurrence of the rebound, and a locking circuit for said alarm control relay.

7. A circuit for testing telephone dials for rebounds of the pulsing contacts thereof comprising a gas-filled triode, an alarm control relay included in the plate circuit of said triode, a source of blocking potential for the control electrode of said triode, a first and second relay whose windings are connected in series with the contacts under test, means controlled by said first relay for completing the connection of said source of blocking potential to the control electrode of said triode, means controlled by said second relay for completing the plate circuit of said tube, said first relay having faster operate and release characteristics than said second relay and said alarm control relay having a time operate characteristic greater than the diiference between the release times of said first and second relays, and an alarm controlled by said alarm control relay.

JOHN H. MCCONNELL. 

